Referring now to FIG. 1, a transimpedance amplifier (TIA) 2 has an input node 4 that is AC coupled through a capacitor 6 to amplifiers 7-1, 7-2, and 7-3, (collectively referred to as amplifiers 7). Each of the amplifiers 7 has a transconductance (gm) and a respective feedback resistance 8-1, 8-2, and 8-3 (collectively feedback resistances 8). An output of the last amplifier 7-3 is coupled to a gate of a transistor 10. An output node 12 produces VOUT and is taken at a source of the transistor 10. A drain of the transistor 10 is connected to a power supply voltage VDD. An AC feedback path is provided to the input node 4 through a feedback capacitor 14 and a feedback resistance 16. A typical capacitance for the feedback capacitor 14 is 35 picofarads (pF). A current source 18 provides a constant current bias IBIAS and is connected between a source of the transistor 10 and a power supply reference voltage VSS.
Referring now to FIG. 1A, a gain of the TIA 2 of FIG. 1 is shown as a function of frequency. It can be seen that the TIA 2 has an undesirably high gain at low frequencies that are identified at 20. The high gain is caused by an impedance of the capacitor 14 at the low frequencies. At higher frequencies that are identified at 22, the capacitor 14 has a lower impedance and the TIA 2 has a flat gain response.